Where does st.file_uploader store uploaded files and when do they get deleted?

When you upload a file using st.file_uploader, the data are copied to the Streamlit backend via the browser, and contained in a BytesIO buffer in Python memory (i.e. RAM, not disk). The data will persist in RAM until the Streamlit app re-runs from top-to-bottom, which is on each widget interaction. If you need to save the data that was uploaded between runs, then you can cache it so that Streamlit persists it across re-runs.

As files are stored in memory, they get deleted immediately as soon as they’re not needed anymore.

This means Streamlit removes a file from memory when:

  • The user uploads another file, replacing the original one
  • The user clears the file uploader
  • The user closes the browser tab where they uploaded the file

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